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  • 1
    Electronic Resource
    Electronic Resource
    Nonlinear optical properties of azo dye monolayers: the effect of tilt angle on the local field (1993)
    s.l. : American Chemical Society
    Langmuir 9 (1993), S. 1974-1977 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00032a011
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of Frenkel excitons in disordered molecular aggregates (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6895-6907 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This article reports on the optical dynamics in aggregates of pseudoisocyanine-bromide and iodide. For PIC-Br in an ethylene glycol/water glass, the results of resonance light scattering (RLS), time-resolved emission, and photon echo decay measurements are discussed. Band structure calculations based on a linear-chain model for the J aggregate have also been performed. The results show that the J band can be described as a disordered Frenkel exciton band in which superradiant states exist that extend over about 100 molecules. Numerical simulation studies of the J band, based on Anderson's Hamiltonian with uncorrelated diagonal site energies, show that the ratio κ of the disorder parameter D over the nearest-neighbor coupling parameter J12 is about 0.11. Using the frequency dependence of the ratio between the yields of vibrational fluorescence and Raman scattering as a probe, the dephasing process and derived parameters for the bath correlation function at three different temperatures have also been examined. It is shown that at all temperatures the exciton dephasing process occurs in the fast modulation limit. For PIC-I in a Langmuir–Blodgett film the optical excitation can be described also in terms of a band transition but the disorder is much larger than in a glass. For this system, a low-temperature fluorescence lifetime of about 10 ps is measured, which suggests that the excitation is much more delocalized than in the case of self-assembled aggregates in a glass. Resonance Rayleigh scattering experiments on PIC in a bilayer show that the exciton-dephasing rate increases dramatically at energies above the renormalized band edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460220
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  • 3
    Electronic Resource
    Electronic Resource
    Optical dephasing in solution: A line shape and resonance light scattering study of azulene in isopentane and cyclohexane (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5477-5484 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of a line shape and resonance light scattering study of the S1←S0 and S2←S0 electronic transitions of azulene in isopentane and cyclohexane are reported. The results are analyzed using two different non-Markovian master equations that make different assumptions about the statistical properties of the bath. For both these origin transitions we find that the solution dynamics fall in the so-called intermediate modulation regime. If exponential decay is assumed for the bath correlation function we obtain a correlation time of the bath of 25 fs for the S1←S0 transition and of 13 fs for the S2←S0 transition at room temperature. From the frequency dependence of the ratio of fluorescence to Raman yields of the S1←S0 transition we calculate an excited state lifetime of 1.4±0.2 ps using the parameters of the bath derived from the line shape analysis, and irrespective of which master equation is used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459617
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  • 4
    Electronic Resource
    Electronic Resource
    Discussion of a "coherent artifact'' in four-wave mixing experiments (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3296-3305 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, we discuss the nonlinear optical effects that arise when stochastic light waves, with different correlation times, interfere in an absorbing medium. It is shown that four-wave mixing signals are generated in several directions that spectrally track the incoming light fields. This effect is particularly relevant to transient hole-burning experiments, where one of these signals could easily be misinterpreted as a genuine hole-burning feature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456905
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  • 5
    Electronic Resource
    Electronic Resource
    Optical dephasing in organic amorphous systems. A photon echo and hole-burning study of pentacene in polymethylmethacrylate (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1-9 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond photon echo experiments on pentacene in polymethylmethacrylate (PMMA) show that the homogeneous width exhibits a T1.3 temperature dependence. This behavior is ascribed to coupling of the pentacene transition to randomly distributed low-frequency excitations in the amorphous host. A calculation of the resulting homogeneous width is presented which uses optical Redfield theory as a starting point. From the results of this calculation we conclude that the coupling between the pentacene molecule and the host low frequency excitations is of static dipolar nature and that the density of states of these excitations varies as ω0.3. Results of nonphotochemical hole-burning experiments on the same system are also reported. Comparison of these results with the ones obtained by the photon echo method indicates, that in the hole-burning experiments, the hole width and its temperature-induced broadening are dominated by spectral diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449809
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  • 6
    Electronic Resource
    Electronic Resource
    The dynamics of one-dimensional excitons in liquids (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 20-33 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The properties of excitons in one-dimensional molecular aggregates, dissolved at room temperature in a liquid, were studied by means of femtosecond nonlinear optical experiments. Both the one-exciton band (i.e., Frenkel-excitons) and multiexciton bands contribute to the observed nonlinear optical response. The rapid motions in the liquid lead to ultrafast perturbations of the molecular energy levels. This localizes the excitons on limited sections of the chains of aggregated molecules. Ultrafast frequency-resolved pump–probe spectroscopy on the lowest two exciton bands was employed to determine the delocalization length of the optical excitations. The kinetics of the exciton populations was measured by ultrafast grating scattering experiments and time-resolved single photon counting. A model is described in which the multiexciton bands act as doorway states in the exciton–exciton annihilation process. These bands thereby determine the population decay of the Frenkel excitons at high excitation densities. Room temperature photon echo experiments show that stochastic perturbations of the exciton transition frequencies occur on two distinct time scales. In particular the slow components of the fluctuations are affected by motional narrowing, associated with the exciton delocalization length. It is therefore argued that the optical dephasing of excitons is directly related to the spatial extent of the excitation on the aggregate chain. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469393
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  • 7
    Electronic Resource
    Electronic Resource
    Low temperature dynamics in amorphous solids: A photon echo study (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6927-6943 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The long-lived stimulated photon echo is put forward as a powerful technique to probe structural dynamics in glasses and other amorphous solids. We present results of optical dephasing measurements on several doped organic glasses (deuterated ethanol, toluene, and triethylamine) and polymers (polystyrene, polyvinylbutyral, and polymethylmethacrylate). Using a stochastic analysis within the so-called two-level-system model, we can extract from these measurements the distribution function of fluctuation rates over a huge range of time scales, varying from picoseconds to hundreds of milliseconds. We show that the dynamics, which lies at the origin of spectral diffusion, is very dependent on the glass structure and can be described by two separate hyperbolic distribution functions of fluctuation rates. From longitudinal photon echo measurements in the population dimension, we find evidence for structural dynamics which is not accounted for in the standard two-level-system model and which is related to a spatially inhomogeneous distribution of fluctuation centers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468321
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  • 8
    Electronic Resource
    Electronic Resource
    Optical properties of disordered molecular aggregates: A numerical study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7880-7890 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of numerical simulations on optical properties of linear molecular aggregates with diagonal and off-diagonal disorder. In contrast to previous studies, we introduce off-diagonal disorder indirectly through Gaussian randomness in the molecular positions; this results in a strongly asymmetric distribution for the interactions. Moreover, we do not restrict to nearest-neighbor interactions. We simultaneously focus on several optical observables (absorption linewidth and line shift and superradiant behavior) and on the density and the localization behavior of the eigenstates (Frenkel excitons). The dependence of these optical properties on the disorder is investigated and expressed in terms of simple power laws. For off-diagonal disorder, such a study has not been performed before. In the case of diagonal disorder, we show that, in particular, the superradiant decay rate of the aggregates may be strongly affected by the inclusion of non-nearest-neighbor interactions. Recent results of absorption line shape, superradiant emission, and resonance light-scattering measurements on pseudoisocyanine aggregates can be understood on the basis of these calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461317
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  • 9
    Electronic Resource
    Electronic Resource
    Femtosecond Twisting and Coherent Vibrational Motion in the Excited State of Tetraphenylethylene (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 8972-8977 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100022a006
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  • 10
    Electronic Resource
    Electronic Resource
    Low-Temperature Protein Dynamics Studied by the Long-Lived Stimulated Photon Echo (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 3913-3916 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100065a056
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